1. Field of the Invention
The present invention relates to a graphic drawing image processing apparatus, and more particularly to a technical field of storing texture data to be applied to a graphic element to be drawn in a built-in memory when a DRAM or other memory and a logic circuit are provided together.
2. Description of the Related Art
Computer graphics are often used in a variety of computer aided design (CAD) systems and amusement machines. Especially, along with the recent advances in image processing techniques, systems using three-dimensional computer graphics are becoming rapidly widespread.
In three-dimensional computer graphics, the color value of each pixel is calculated at the time of deciding the color of each corresponding pixel. Then, rendering is performed for writing the calculated value of the pixel to an address of a display buffer (frame buffer) corresponding to the pixel.
One of the rendering methods is polygon rendering. In this method, a three-dimensional model is expressed as a composite of triangular unit graphics (polygons). By drawing the polygons as units, the colors of the display screen are decided.
In polygon rendering, coordinates (x, y, z), color data (R, G, B,), homogeneous coordinates (s, t) of texture data indicating a composite image pattern, and a value of the homogeneous term q for the respective vertexes of the triangle in a physical coordinate system are input and processing is performed for interpolation of these values inside the triangle.
Here, the homogeneous term q is, simply stated, like an expansion or reduction rate. Coordinates in a UV coordinate system of an actual texture buffer, namely, texture coordinate data (u, v) are comprised of the homogeneous coordinates (s, t) divided by the homogeneous term q to give “s/q” and “t/q” which in turn are multiplied by texture sizes USIZE and VSIZE, respectively.
FIG. 15 is a view of the system configuration showing a basic concept of a three-dimensional computer graphic system.
In this three-dimensional computer graphic system, data of drawing graphics is supplied from a main memory 2 in a main processor 1 or from an input/output (I/O) interface circuit 3 for receiving graphic data from outside via a main bus 4 to a rendering circuit 5 having a rendering processor 5a and a frame buffer memory 5b. 
In the rendering processor 5a, a frame buffer memory 5b for maintaining data for display and a texture memory 6 for maintaining texture data to be applied on the surface of a graphic element (for example, a triangle) to be drawn are connected.
Then, the rendering processor 5a performs processing for drawing the graphic element applied with the texture on its surface for every graphic element to the frame buffer memory 5b. 
The frame buffer memory 5b and the texture memory 6 are generally configured by a DRAM (dynamic random access memory).
In the system of FIG. 15, the frame buffer memory 5b and the texture memory 6 are configured as physically separated memory systems.
Note that, even after it became possible to provide the DRAM and a logic circuit together, to hold the texture data inside has been difficult due to both the limit of the DRAM capacity and the processing speed.
In the so-called built-in DRAM system of the related art above, when the frame buffer memory and the texture memory are provided separately in separate memory systems, there are the disadvantages as stated below:
First, the frame buffer memory which is emptied due to a change of the display resolution cannot be used as a texture memory.
This becomes a big disadvantage when trying to perform all of the processing in the limited capacity of a built-in DRAM.
Second, when making the frame buffer memory and the texture memory physically identical, in simultaneous access to the frame buffer memory and the texture memory, the overhead of switching pages of the DRAM etc. becomes large, so the performance has to be sacrificed.
These disadvantages are not particularly limited to a graphic drawing apparatus of a built-in DRAM type and have been disadvantages in systems of an externally provided DRAM type as well, but have not been as serious as the built-in type where the capacity is strictly limited.